1. Field of this invention
The present invention relates to a method for decreasing the cyclic oligomer content in polyester products, which improves the method disclosed in our U.S. Pat. No. 6,392,005. More particularly, the present invention relates to a method for decreasing the cyclic oligomer content in polyester products by adding other chemicals during the manufacturing process of polyethylene terephthalate (hereafter xe2x80x9cPETxe2x80x9d), which further restrain the cyclic oligomer residue in the chips and decrease the amount of regenerated cyclic oligomer at the rear-end stage melting process. The resulting PET material is then transformed into products such as polyester bottles, polyester fibers, polyester films, and polyester laminate structures through different manufacturing processes.
2. Description of Prior Art
PET is well known as a heat plasticized plastic material having good physical characters and a capable of being recycled. Thus, PET is widely used in manufacturing products such as polyester bottles, polyester fibers, polyester films, and polyester laminate structures, which renders PET an extremely valuable plastic material.
However, during the process of manufacturing PET cyclic oligomers having low molecular weight, particularly those oligomers exhibiting white crystallized powder characteristics, are produced from side reaction. These cyclic oligomers with a melting point of above 300xc2x0 C. usually pollute the mold equipment while being processed, and further adhere to the final, processed polyester products. Consequently, the production line is often shut down and cleaned from time to time. Moreover, during the high temperature heat crystallization process in which the PET is transformed into heat-filling resistance bottles and the crystallization temperature and the heat filling temperature are above 80xc2x0 C., most of the residual cyclic oligomers in the PET or the cyclic oligomers regenerated during processing are often transferred to the surface and/or frequently enter into the packaged contents which may be hazardous to human health.
To solve the cyclic oligomer problem, we disclosed in U.S. Pat. No. 6,392,005 adding - during the melting process of PET - a compound (hereinafter called P1) containing phosphorus in an amount of between 50-3000 ppm based on the total weight of the PET, which effectively decreased the cyclic oligomer content in the PET chips and their respective manufactured products. The compound proposed in our previous patent has the following structure: 
Below we list examples of prior art and/or publications that have suggested ways of decreasing the cyclic oligomer content in PET chips and their respective manufactured products thereof:
(1) Japan publication No. 12-219731 discloses that addition of SO3X compound effectively restrains the produced cyclic oligomer content in polymerized PET in the melted state;
(2) Japan publication No. 12-204229 discloses that addition of alkali metals or alkaline-earth metals such as calcium acetate or magnesium benzoate into PET containing germanium catalyst can effectively restrain the cyclic oligomer content;
(3) Japan publication No. 12-219729 discloses that when each mole of PET contains between 0.5xc3x9710xe2x88x924xe2x88x924xc3x9710xe2x88x924 moles of antimony element and between 1xc3x9710xe2x88x924xe2x88x925xc3x9710xe2x88x924 moles of phosphoric acid, the mole ratio of the antimony element to the phosphorus element is between 1-3 and the cyclic oligomer content is effectively restrained;
(4) Japan publication No. 12-198937 discloses that when the germanium element is between 0.5xc3x9710xe2x88x924-4xc3x9710xe2x88x924 moles relative to the acid component of the PET the phosphoric acid is added until the phosphorus element is between 1xc3x9710xe2x88x924xe2x88x927xc3x9710xe2x88x924 moles relative to the acid component of the PET, at which time the mole ratio of the germanium element to the phosphorus element is greater than 1.6 and thus effectively restrains the cyclic oligomer content;
(5) Japan publication No. 12-80284 discloses melt blending the PET chips with heat-plasticized-resin master batch, which contains one of the following three structural compounds: alkylene oxide, polyalkylene glycol or bisphenol. The analyzed cyclic oligomer content of the PET resin observed is much lower than the PET resin obtained from similar process without these compounds;
(6) Japan publication No. 11-80520 discloses that less pollution exist in the blow molding equipment during blow-molding when amide compounds are added into the solid- state polymerized PET;
(7) Japan publication No. 10-168168 discloses a process for producing the PET chips containing between 2xcx9c4 wt% of diethylene glycol by using an amorphous state germanium dioxide as a catalyst. The time to add the amorphous state germanium dioxide catalyst is when the esterification reaction ratio reaches above 90% , so as to reduce the production of formaldehyde, acetaldehyde, and cyclic oligomers during the injection-molding process;
(8) Japan publication No. 10-110026 discloses that the addition of alkaline metals and alkaline earth metals such as lithium acetic, calcium acetic can restrain the cyclic oligomer content of ester chips and their manufactured bottles thereof;
(9) Japan publication No. 9-221540 discloses that when the diethylene glycol (DEG) content of the PET chips is between 1-4 mole%, the intrinsic viscosity is between 0.60-0.90 dl/g, the phosphoric acid content based on the total weight of the PET is between 5-25 ppm, the content of the germanium element based on the total weight of the PET is between 20-60 ppm, and the mole ratio of the germanium element content to the phosphorus element content is between 0.4-1.5, the polyester material processed has a low cyclic oligomer content level;
(10) Japan publication No. 9-296029 discloses that for PET containing germanium catalyst, when the alkaline-earth metal atom content based on the PET is between 1xc3x97104xe2x88x925xc3x9710xe2x88x923 moles, the cyclic oligomer content in the PET is low and the regenerated cyclic trimer from the melting process is considerably small;
(11) Japan publication No. 59-25815, 3-174441, 6-234834, and 3-47830 disclose a specific process to reduce oligomers in PET by placing the PET into boiling water, thereby reducing the residual cyclic oligomers in the PET chips and the regenerated cyclic oligomers during processing;
(12) U.S. Pat. No. 6,020,421 discloses the use of a PET composition containing a metal atom A and a phosphide containing a valance of 5, wherein the metal atom A can be an antimony atom, a titanium atom, or a germanium atom, and the phosphide can be selected from the phosphate group consisting of an orthophosphoric acid salt, a metaphosphoric acid salt, a polymetaphosphoric acid salt (HPO3)m (where mxe2x89xa73), and a polyphosphoric acid Hn+2PnO3n+1 ( where nxe2x89xa72);
(13) U.S. Pat. No. 5,948,458 discloses that the addition of phosphate into the plastic used for wrapping food creates an ultraviolet ray resistance effect in the plastic which help preserves the integrity and coloration of food; however, this patent does not disclose any cyclic oligomer content issues.
(14) U.S. Pat. No. 5,744,572 discloses the addition of carboxy phosphonic acid which catalyzes the reaction rate of polyester; however, it did not mention the effect on cyclic oligomer contents.
All of the aforementioned prior arts and/or publication do not mention the addition of a calcium phosphate compound having a Ca3(PO4)2 structure or a Ca5OH(PO4)3 structure or the simultaneous addition of a phosphoric ester having structure (1), or the addition of two or more than two compounds in order to restrain the cyclic oligomer content in the PET chips and their related manufactured products thereof.
An object of this invention is to disclose a manufacturing method and compounds added thereof capable of greatly reducing the cyclic oligomer content in manufactured PET chips, as compared to the manufacturing method and compounds thereof disclosed in U.S. Pat. No. 6,392,005.
Another object of this invention is to disclose an additive, a calcium phosphate compound and a carboxy phosphonic acid compound capable of reducing the cyclic oligomer content in manufactured PET chips, wherein the calcium phosphate is selected from the group consisting of a Ca3(PO4)2 structure and a Ca5OH(PO4)3 structure, and the carboxy phosphonic acid compound has a structure (1) as follows: 
wherein R1, R2, and R3 are alkyls or hydrogen atoms and R is an alkyl.
Still, another object of this invention is to disclose that addition of the calcium phosphate compound or the carboxy phosphonic acid having structure (1) of the present invention into the polymerization-reaction manufacturing stage of the PET material decreases the cyclic oligomer residues in the resulting PET chips, and effectively restrains the regeneration of cyclic oligomers during processing.
Yet, another object of this invention, which is a preferred embodiment of the present invention, is to disclose that the simultaneous addition of the calcium phosphate compound and the compound having structure (1) of the present invention, during the melt-polymerization manufacturing stage of the polyester chips, results in the producing of polyester material and their related polyester products thereof containing less cyclic oligomer content than the process disclosed in U.S. Pat. No. 6,392,005.
A further object of this invention, which is a preferred embodiment of the present invention, is to disclose that the addition of the calcium phosphate compound and the compound having structure (1) of the present invention and the PI compound disclosed in our U.S. Pat. No. 6,392,005 results in a decrease in the cyclic oligomer content in the obtained PET chips and their related processed products thereof.
Yet, a further object of this invention is to disclose that the novel manufacturing methodology disclosed by the present invention appropriately decreases the addition amount of the PI compound disclosed in our U.S. Pat. No. 6,392,005 and results in overall reduction in manufacturing cost.
Other objects, aspects, advantages and novel features of the invention detail will become more apparent from the following description.